This invention relates an environmental sensor. This invention also relates to a method of operating an environmental sensor.
Environmental sensors can be used for the determination of various physical parameters such as temperature, light intensity, pressure, strain, shock, moisture, carbon dioxide and many other gases in various environments such as buildings (e.g. houses, offices, warehouses, green houses etc.), vehicles such as cars and trucks (for example in the passenger compartment, or in the engine of the vehicle), in-vitro and even in-vivo applications.
There is a clear society trend to make homes and building smart, meaning that the ecological footprint of homes and buildings must be reduced as much possible. A lot of energy in buildings and homes is used in heating, ventilation and air conditioning (HVAC). A carbon dioxide sensor can, for example, monitor the quality of the air and together with a temperature and humidity sensor feedback the results to the HVAC system that then can take appropriate actions. Additional energy reduction can be achieved by environmental sensors that measure the light intensity in a room and adjust the artificial lighting accordingly. All these environmental sensors can also be connected through networks. In this way lighting, temperature, fresh air and humidity can be dynamically adjusted rather than following a pre-programmed regime and in this way the ecological footprint can be reduced.
It is also very well thinkable that environmental sensors such as pressure, airborne particles, carbon dioxide, and carbon monoxide sensors, and sensors to monitor breath composition will increasingly appear in mobile devices such as mobile telephones or tablets.
Another application domain is in the car, where the drivers and passengers want to monitor the quality of air for contaminants and particles and where the control systems then can take appropriate action such as shutting down or filtering in coming air.
Another application domain is in the white good market segment. For example, moisture and grease layers in refrigerators can indicate the level of hygiene in the refrigerator. An environmental sensor in the refrigerator, that can monitor levels of for example NH3 or other freshness of food related gases, can malfunction in case moisture or grease layers accumulate.
In many of these applications the sensors will be used for years, aiming for undisturbed functioning as an autonomous device. During that time and while exposed to the ambient it is very well possible that the surface of the sensor will see a deposit of materials such as dust, oil, salt, grease etc. For optical (light intensity measurements) as well as chemical sensors (moisture, gases, liquids) and mechanical sensors (e.g. MEMS based devices) such as pressure sensors including a diaphragm, these fouling layers can severely impact proper reading of the parameter.
Although there have been reports on the detection of fouling layers (U.S. Pat. No. 5,998,782; EP 1457763; DE 102006039034, JP 2002296342, U.S. Pat. No. 8,144,330 and U.S. Pat. No. 7,652,586) none of those are in the field of environmental sensors.